Preparation of a dye for coloring protein-based fibers and cellulose-based materials from the oxidation products of the manufacture of a triphenylmethane dye

ABSTRACT

A process of preparing a dye composition and a resultant dye composition. The process includes preparing a mixture comprising a triphenylmethane dye and oxidation products by reacting methylenedianiline, aniline, an oxidation catalyst, and an oxidant; separating the oxidation products from the triphenylmethane dye to produce an aqueous solution of oxidation products; treating the solution of oxidation products with a basic compound; separating unreacted aniline from the solution of oxidation products and forming a mixture of oxidation products; and sulfonating the mixture of oxidation products to form a dye composition.

FIELD OF THE INVENTION

The present invention relates to a process of preparing a dyecomposition from the oxidation products of the synthesis of atriphenylmethane dye, such as pararosaniline, and more particularly to aprocess where the products of the triphenylmethane dye synthesis arerendered water soluble and suitable for application as dyes or colorantsto various protein-based fibers and cellulose-based materials. Theinvention further relates to dye compositions formed by such processes,methods of dyeing fibers and fabrics with the dye compositions of theinvention, and the dyed materials produced thereby.

BACKGROUND AND SUMMARY OF THE INVENTION

Triphenylmethane dyes, such as pararosaniline, may be prepared byoxidation of the condensation products of excess aniline withformaldehyde. Pararosaniline, also known as fuchsin, parafuchsin, BasicRed 9, Magenta 0, and C.I. 42500, is commercially produced via thissynthesis with formation of by-products or oxidation products that have,up to this time, had no commercial value. The by-products of thetriphenylmethane dye synthesis have found only limited application ascolorants in situations where the by-product could be melted and blendedwith the substance to be colored. The by-products were also employed ascolorants by dispersing them in a mixture with a solid resin or likematerial, as in, for example, U.S. Pat. No. 3,884,869, incorporatedherein by reference. Thus, the by-product mixture could only be used asa pigment and modification of the by-products for use as a dye wasunknown.

The present invention provides a process of preparing a dye compositionwhich employs oxidation products (typically referred to as by-products)of a triphenylmethane dye synthesis and a resultant dye composition. Theprocess includes preparing a mixture of a triphenylmethane dye and theoxidation products by reacting methylenedianiline with aniline, anoxidation catalyst, and an oxidant. Oxidation by-product as used hereinis to be understood to mean the desired oxidation products of thecondensation reaction, and subsequent oxidation, of methylenedianilinethat are employed as the dye composition of the present invention.

The process further includes separating the oxidation products from thetriphenylmethane dye to produce a solution of oxidation products;treating the solution of oxidation products with a basic compound, whichis typically dissolved in water; separating unreacted aniline from thesolution of oxidation products to form a mixture of oxidation products;and sulfonating the mixture of oxidation products to form a dyecomposition.

The present invention also provides a process of dyeing protein-basedfibers and the resultant colored protein-based fibers. The processincludes providing a dye composition prepared according to the processsteps as set forth above; immersing the protein-based fibers in acontainer of water and an acid; dissolving the dye composition in aseparate container of water, producing a dye solution; adding to the dyesolution sodium sulfate and an acidic compound, such as acetic acid,sulfuric acid, propionic acid, phosphoric acid, and mixtures thereof;and stirring the protein-based fibers into the dye solution and heatingthe solution to produce colored protein-based fibers. The fibers may be,but are not limited to, textile fibers, such as wool and silk, andcarpet fibers.

The present invention additionally provides a process of dyeingcellulose-based materials and the resultant colored cellulose-basedmaterials. The process includes providing a dye composition preparedaccording to the process steps as set forth above; immersing thecellulose-based fibers in a container of water; dissolving the dyecomposition in a container of water, producing a dye solution; adding tothe dye solution sodium sulfate and an acidic compound, such as aceticacid, sulfuric acid, propionic acid, phosphoric acid, or a mixture ofthese acids; and soaking the cellulose-based materials in the dyesolution and heating the solution to produce colored cellulose-basedmaterials.

The present invention also provides a dye composition comprisingsulfonated oxidation products that produces a variety of hues for dyeingprotein-based fibers and cellulose-based materials. In addition, the dyecomposition is resistant to fading from both light and washing, and hasa low-cost of manufacture.

DETAILED DESCRIPTION

A process of preparing a dye composition has now been discovered. Thecomposition comprises the sulfonated oxidation products or by-productsof a process for synthesizing a triphenylmethane dye, and mostpreferably comprises the sulfonated oxidation products or by-products ofpararosaniline.

The oxidation by-products of the present invention may be formed byoxidizing the various compounds of methylenedianiline produced in thesynthesis of pararosaniline. The oxidation by-products of this synthesisare believed to be a mixture of compounds structurally similar toacridines, phenazines, phenosafranines, or the various aniline blacks.The by-product composition of the pararosaniline synthesis may then berendered water soluble by sulfonation and applied as a dye or colorantto various protein-based fibers, such as wool and silk, and tocellulose-based materials, such as wood pulp and cotton.

The process of preparing a dye composition of the present inventionincludes treating aniline with an acid. Preferred acids include, withoutlimitation, hydrochloric acid, anhydrous hydrogen chloride, aqueoushydrochloric acid, acetic acid, and mixtures of these. The reactionproduces an aniline acid salt, such as an aniline hydrochloride salt,having a degree of protonation ranging from less than about 10% togreater than about 90%. This salt is then reacted with a source offormaldehyde in a preferred ratio of about two moles of salt to aboutone mole of formaldehyde to form methylenedianiline. The source offormaldehyde preferably includes a formalin solution, gaseousformaldehyde or solid paraformaldehyde. Among the products of thisreaction are various isomers of methylenedianiline, for example, 4,4'-methylenedianiline and 2, 4-methylenedianiline. The condensationreaction of aniline and formaldehyde generally produces these isomers ina ratio of approximately 65% 4, 4'-methylenedianiline isomer and 34% 2,4-methylenedianiline isomer. Additional compounds may also be produced,such as aniline compounds and a multi-ring compound.

The mixture of methylenedianiline compounds and additional compounds isthen oxidized by adding an oxidation catalyst, aniline, and an oxidant.The oxidation reaction produces a mixture comprising a triphenylmethanedye and oxidation by-products. The oxidation of methylenedianiline to atriphenylmethane dye typically requires at least two to three moles ofaniline, which also provides a solvent effect for the reaction products.In addition, a portion of the aniline is oxidized to form minorcomponents of the by-product dye composition, such as aniline blackcompounds.

The oxidation catalyst used in the present process is preferably, butnot limited to, a catalyst including any element from groups VB and VIB,such as vanadium or molybdenum. A vanadium oxide catalyst, as disclosedin U.S. Pat. No. 2,542,544, incorporated herein by reference, is mostpreferably used in the synthesis of the present invention. The oxidationcatalyst may include sodium metavanadate, ammonium metavanadate,vanadium(IV) oxychloride, vanadium(V) oxychloride, and mixtures ofthese. The oxidant employed is preferably air, oxygen, or oxygenenriched air.

The reaction in which the 4, 4'-methylenedianiline is formed ispreferably carried out with a ratio of aniline to formaldehyde at thebeginning of the reaction of greater than 2:1, a temperature of fromabout 10 to about 100° C., and with greater than or equal to about 5% ofthe aniline being protonated. This 4, 4'-methylenedianiline isomerproduces pararosaniline and a small proportion of the dye composition ofthe present invention. For example, the oxidation of 4,4'-methylenedianiline may form approximately 85% pararosaniline and only15% of the oxidation by-products used for the present dye composition.The oxidation of the 2, 4-methylenedianiline isomer, however, producesthe major component of the by-product dye composition in the form of,for example, compounds with structures similar to acridine compounds. Athree-ring compound is also believed to be formed during the synthesisof the triphenylmethane dye and is oxidized to become a part of theoxidation by-products used to produce the dye of the present invention.

As will be fully appreciated by the skilled artisan, the proportion ofisolated pararosaniline to oxidation by-products may be adjusted byvarying the conditions under which the oxidation reaction occurs,including temperature, pressure, time of reaction, catalyst level andtype, and oxidant concentration. For example, the conditions mostfavorable to pararosaniline formation are temperatures of at least about90 and up to about 120° C., pressures of at least about 20 and up toabout 100 psi, catalysts levels (such as vanadium or molybdenumcatalysts) of greater than 1.5 millimoles per mole ofmethylenedianiline, and an increased oxygen content.

The triphenylmethane dye synthesized by the process of the presentinvention is preferably, but not limited to, pararosaniline. Anytriphenylmethane dye that is synthesized by condensing at least 2 molesof an aminobenzene-based compound onto at least one mole of formaldehydeand then oxidizing the condensation product is included within the scopeof this invention. Examples of dyes that have similar properties andapplications may include Acid Violet 4BN, Acid Violet 3BN, Acid Violet R(extra), Acid Blue 15, Acid Violet 17, Acid Violet 23, Acid Violet 72,Food Violet 1, Mordant Violet 39, Mordant Violet, 27, and Mordant Violet33.

According to a preferred embodiment of the present invention, first asolution of oxidation by-products is produced when the oxidationby-products are separated from pararosaniline. The step of separatingthe oxidation by-products from the triphenylmethane dye may beaccomplished by a variety of methods. One preferred way to separate theby-products is by adjusting the pH of said mixture to about 7 bytreating said mixture with a basic compound, such as sodium hydroxide,and water; converting the triphenylmethane dye to an insoluble form, forexample, by adding an anion, such as, but not limited to, nitrate,bisulfate or cyanide; and then filtering the mixture to remove theinsoluble triphenylmethane dye. The anion employed may be any anion thatmakes the triphenylmethane dye insoluble in aniline.

Another preferred method of separation is by adding a solvent to themixture in which the triphenylmethane dye is insoluble and the desiredoxidation by-products are soluble, followed by filtering the mixture toremove the triphenylmethane dye. The solvent employed may be any benzeneor alkyl-substituted benzene compound, such as, but not limited to,toluene, cumene, xylene, and ethyl benzene.

The filtrate, which is the desired solution of oxidation by-products,may then be further processed by adding to the solution a basiccompound, which is typically dissolved in water. The basic compound thatis added is preferably, but not limited to, sodium hydroxide. Asufficient amount of basic compound, and preferably water, is added toadjust the pH to at least about 10.5, preferably to a lower limit ofabout 12 and to an upper limit of about 13.8. This allows the removal ofany inorganic salts present in the solution, particularly nitrates andchlorides, from the organic phase by a phase separation.

A mixture of oxidation by-products or products is formed by separatinganiline from the solution of oxidation products. The aniline ispreferably separated by, but not limited to, distillation. Less than 1%of unreacted aniline is preferably remaining in the solution afterdistillation. The mixture of oxidation by-products may then be treatedby grinding, for example, to form a powder.

The mixture of oxidation by-products is then sulfonated. The sulfonationstep of the present invention is carried out by adding concentratedsulfuric acid to the dye composition and heating the mixture. Themixture is preferably heated to from about 40 to about 90°C., and mostpreferably to from about 50 to about 80° C. The sulfonation of themixture of oxidation by-products renders the by-products water solubleand capable of being permanently bound to protein-based fibers andcellulose-based materials. The sulfonated oxidation by-products arelarge, multi-ring structures that are effective as dyes for coloring,for example, yarns made from wool and wood pulp. In addition, thesulfonation step dissolves the remaining unsulfonated, water solublesalts of 4, 4'-methylenedianiline and aniline, so that they may beseparated and washed out.

The compounds of the by-product mixture may be mono- or polysulfonateddepending on their various structures and the conditions of thesulfonation process of the present invention. For example, decreasedtemperatures of 25-35° C. and the use of 95-98% sulfuric acid favors theformation of monosulfonated compounds, whereas increased temperatures,such as about 40-80° C. and higher concentration levels of sulfonatingagents, such as oleum, produce greater amounts of polysulfonatedmaterials. The monosulfonated by-product compounds are the preferredcomponents of the by-product dye composition because the polysulfonatedcomponents are more water soluble and, subsequently, harder to isolatethan the monosulfonated components.

Protein-based fibers may be dyed using the sulfonated oxidationby-product dyes. The fibers include, but are not limited to, textilefibers, such as wool and silk, and carpet fibers. The process of thepresent invention may additionally be used to dye or color woven fabric.

The process for dying these fibers includes preparing a dye compositionaccording to the process of the present invention, and then immersingthe fibers in a container of water and an acid, such as acetic acid oraqueous hydrochloric acid. The dye composition is then dissolved in aseparate container of water, producing a dye solution to which sodiumsulfate and an acidic compound is added in an amount of about 1-15% ofthe weight of the fiber. The acidic compound includes, but is notlimited to, any short-chained (C₁ to C₁₀) carboxylic acid, such asacetic acid or propionic acid; any hydrates of sulfur trioxide, such assulfuric acid or oleum; phosphoric acid; polyphosphoric acid; andmixtures of these. The acidic compound is utilized as a levelling agentfor the dye, aiding in the uniform dispersion of the dye in solution.The fibers are stirred into the dye solution and the solution is heatedto from about 80 to about 100°C., producing colored protein-basedfibers. The fibers may be dyed, for example, dark brown, golden brown,and reddish brown, depending on the conditions of the reaction, such asthe acid used in the dye pot during the dyeing procedure.

Cellulose-based materials may be dyed with the compositions of thepresent invention to produce colored cellulose-based materials. Thematerials are preferably, but not limited to, wood pulp and cotton. Theprocess includes preparing a dye composition according to the process ofthe present invention, and then immersing the cellulose-based materialsin a container of water. The dye composition is also dissolved in aseparate container of water, producing a dye solution to which sodiumsulfate and an acidic compound is added in an amount of about 1-15% ofthe weight of the material. The acidic compound includes, but is notlimited to, any short-chained (C₁ to C₁₀) carboxylic acid, such asacetic acid or propionic acid; any hydrates of sulfur trioxide, such assulfuric acid or oleum; phosphoric acid; polyphosphoric acid; andmixtures of these. The cellulose-based materials are then soaked in thedye solution, and the solution is heated to from about 80 to about 100°C., producing colored cellulose-based materials.

The invention is further described in the following examples. Theexamples are merely illustrative and do not in any way limit the scopeof the invention as described and claimed.

EXAMPLES Example 1

Preparation of the By-Product Residue Used in Preparing the DyeComposition

Add 11,837 grams (127.28 moles) of aniline and 2031 grams of 32%hydrochloric acid (17.8 moles) to a reaction vessel, allow to stir, andadd, as rapidly as possible, 1085 grams of 35% formalin (12.64 moles).Heat this reaction mass to 130° C. and maintain this temperature over athree hour period. Cool to 110° C. and add 1.5 millimoles of sodiummetavanadate per mole of formaldehyde. Blow 90 psig air through the massfor 2.5-3.5 hours. Add 3300 grams of water and a sufficient amount of50% sodium hydroxide solution to reach a pH of about 7. Allow the massto stand for one hour and then separate the water layer from thereaction mass.

Add 1850 grams of a solution of sodium nitrate (950 grams of sodiumnitrate, 11.18 moles, in 1900 grams of water) at 90° C. to the reactionmixture. Vacuum distill the water out of the reaction mass whilemaintaining gentle agitation over a period of two hours to form crystalsof pararosaniline nitrate as the water is removed. Filter this mass toremove the crystals, which are separately processed to makepararosaniline.

The filtrate aniline solution of oxidation by-products is treated withan equal volume of 18% sodium hydroxide solution to remove any inorganicsalts, specifically nitrates and chlorides, present in the organicphase. Phase separate, keeping the organic phase and discarding theaqueous phase. Vacuum distill the organic phase until a solid residuecontaining less than 2% aniline by weight is obtained. Cool this residueof oxidation by-product mixture and grind it to a fine powder.

Example 2

Sulfonation of the Ground Residue of Oxidation By-Products

Add 95 ml of 98% H₂ SO₄ to a 1000 ml 3-neck flask and cool to 15° C. inan ice bath. Slowly add 50 g of ground residue prepared according toExample 1 to the flask while the mixture is stirred. Remove the ice bathand heat the reaction mixture to 40° C. Add 15 ml of H₂ SO₄ to the flaskand check a sample of the reaction mixture for evidence of sulfonation.If no sulfonation has occurred, add an additional 10 ml of H₂ SO₄ to theflask and increase the heat to 50° C. If the sample still shows noevidence of sulfonation, make further 10 ml additions of H₂ SO₄ to theflask while the temperature is increased to 80° C. until sulfonationoccurs. Add the reaction mixture into three liters of water and filterthe solution. Retain the filter cake and aqueous filtrate prepared fromthe residue for use as a dye composition.

Procedure for Dying Wool Yarn with the Sulfonated Oxidation By-Productsin Examples 3-7

Wash 100% virgin wool yarn, or similar fiber material, that has been dryweighed and soak the fiber material in hot water containing soap atapproximately 50° C. Enough soap should be used to make the waterslippery without producing suds. The fiber material should soak for ashort time, such as 15-20 minutes, in the hot water. Next, hot watersoak the fibers at approximately 50° C. Rinse the fibers in hot waterand 0.5% acetic acid and soak the material for a short time, such as 15minutes, in a dilute acetic acid solution (about 1 ml acetic acid inabout 200 ml of water). Soak the fibers in clean hot water (50° C.) andrepeat the clean hot water soak if traces of soap are evident. If thefibers subsequently dry, soak them in warm water for at least 20 minutesand squeeze out excess water before placing the fibers in a dye pot.

Next, dissolve an amount of the sulfonated ground residue dyecomposition prepared according to Examples 1 and 2 in 50° C. water (30ml of water per gram of dry fiber weight) and add sodium sulfate at 20%of the weight of dry fiber used. (Weight of fiber×0.20=weight of sodiumsulfate to use.) Stir the solution to dissolve the added components andadd about 4% acetic acid (by weight of the fiber). Mix the wetted fibersinto the solution and heat the solution to about 80° C. over a 15 minuteperiod, stirring frequently. Continue to heat the solution to about95-100° C. and hold at that temperature for 45 minutes. Stir thesolution occasionally.

Lastly, allow the fibers to cool before washing with a neutraldetergent. Rinse the fibers thoroughly, remove any excess water, and drythe fibers.

Example 3

The sulfonated filtrate prepared according to the procedure in Example 2was used as the dye composition to dye wool fibers. The pH of thefiltrate was adjusted to 6.5 with 50% NaOH and acetic acid was added toadjust the pH to about 2.00. This solution was filtered. 4.33 g of dryfiber was washed, dried, and dyed according to the above procedure,adding 129.9 ml of filtrate (30 ml of the filtrate solution per gram ofdry fiber) and 0.9 g of sodium sulfate to a dye pot. The resulting dyedfibers were a deep, dark brown color.

Example 4

The filter cake from the sulfonated residue prepared according to theprocedure in Example 2 was dried and used to prepare the dyecomposition. 6.00 g of dry fiber was washed, dried, and dyed accordingto the wool dyeing procedure above, adding 0.6 g of ground filter cake,180 ml of water, 1.2 g of sodium sulfate, and 0.4 g of acetic acid (7%by weight of fiber) to the dye pot. The resulting dyed fibers were alight, golden brown color.

Example 5

The wet filter cake from the sulfonated residue according to theprocedure of Example 2 was used for the dye composition. 7.04 g of dryfiber was washed, dried, and dyed according to the wool dyeingprocedure, adding 1.03 g of wet filter cake, 210 ml of water, 1.4 g ofsodium sulfate, and 0.46 g of acetic acid (6.5% by wt. of fiber) to thedye pot. The resulting dyed fibers were a rich, reddish brown color.

Example 6

Use of Sulfuric Acid in Dye Pot

1-2% of concentrated sulfuric acid (to wt. of fiber) was used in placeof acetic acid for leveling the dye composition. The weight of H₂ SO₄used was 11% of the weight of fiber used.

The dried filter cake from the sulfonated residue according to theprocedure of Example 2 was used. 1.6 g of fiber was washed, dried, anddyed according to the wool dyeing procedure, adding 0.16 g of driedfilter cake, 48 ml of water, 0.32 g of sodium sulfate, and 0.18 g ofsulfuric acid to a dye pot.

After 45 minutes of dyeing the fiber, the fiber was "top-chromed" bydissolving 3% (of wt. of fiber) of sodium dichromate in 10 ml water.Several ml of cool water at 78° C. was added to the dye pot. The fiberwas stirred occasionally while the temperature was heated to 95-100° C.for 60 minutes. The yarn was then cooled, washed in cool water with asmall amount of mild soap without suds and rinsed well. The resultingdyed fibers were a deeper, darker brown as compared to Examples 3-5.

Example 7

Use of Dried Filter Cake From the Sulfonated Residue for the DyeComposition

The fibers here were dyed according to the procedure in Example 6,except the "top-chroming" procedure was eliminated.

1.5 g of fiber was washed, dried, and dyed according to the wool dyeingprocedure, adding 0.15 g of the filter cake, 45 ml of water, 0.165 g ofconcentrated sulfuric acid, and 0.3 g of sodium sulfate. The resultingdyed fibers were a medium reddish brown color.

The invention has been described in detail with reference to preferredembodiments thereof. It should be understood, however, that variationsand modifications can be made within the spirit and scope of theinvention.

What is claimed is:
 1. A process of preparing a dye composition,comprising the steps of:(a) preparing a mixture comprising atriphenylmethane dye and oxidation products by reactingmethylenedianiline, aniline, an oxidation catalyst, and an oxidant; (b)separating said oxidation products from said triphenylmethane dye toproduce an aqueous solution of oxidation products; (c) treating saidsolution of oxidation products with a basic compound; (d) separatingunreacted aniline from said solution of oxidation products to form amixture of oxidation products; and (e) sulfonating said mixture ofoxidation products to form a dye composition.
 2. A process according toclaim 1, wherein said triphenylmethane dye is pararosaniline.
 3. Aprocess according to claim 1, wherein said methylenedianiline is anisomer selected from the group consisting of 2, 4-methylenedianiline, 4,4'-methylenedianiline, and mixtures thereof.
 4. A process according toclaim 1, wherein said oxidation catalyst is a vanadium oxide catalyst.5. A process according to claim 4, wherein said vanadium oxide catalystis selected from the group consisting of sodium metavanadate, ammoniummetavanadate, vanadium(IV) oxychloride, vanadium(V) oxychloride, andmixtures thereof.
 6. A process according to claim 1, wherein saidoxidant is selected from the group consisting of air, oxygen, oxygenenriched air, and mixtures thereof.
 7. A process according to claim 1,wherein said separation step (b) is carried out by:(a) adjusting the pHof said mixture to about 7 by treating said mixture with a basiccompound and water; (b) converting said triphenylmethane dye to aninsoluble form with an anion selected from the group consisting ofnitrate, bisulfate, cyanide, and mixtures thereof; and (c) filteringsaid mixture to remove said triphenylmethane dye.
 8. A process accordingto claim 1, wherein said separation step (b) is carried out by:(a)adding to said mixture a solvent in which said triphenylmethane dye isinsoluble and in which said oxidation products are soluble; and (b)filtering said mixture to remove said triphenylmethane dye.
 9. A processaccording to claim 8, wherein said solvent is a benzene oralkyl-substituted benzene compound.
 10. A process according to claim 1,wherein said basic compound is sodium hydroxide.
 11. A process accordingto claim 1, wherein said sulfonation step (e) is carried out by addingsulfuric acid to said mixture of oxidation products and heating saidmixture to from about 40 to about 90° C.
 12. A process according toclaim 1, wherein said oxidation products are based on the structures ofcompounds selected from the group consisting of acridines, phenazines,phenosafranines, aniline blacks, and mixtures thereof.
 13. A processaccording to claim 1, wherein said mixture of oxidation products in step(d) is treated to form a powder.
 14. A process of dyeing protein-basedfibers, comprising the steps of:(a) providing a dye composition preparedaccording to claim 1; (b) immersing said protein-based fibers in acontainer of water and an acid; (c) dissolving said dye composition in aseparate container of water, producing a dye solution; (d) adding tosaid dye solution sodium sulfate and an acidic compound; and (e)stirring said protein-based fibers into said dye solution and heatingsaid solution to produce colored protein-based fibers.
 15. A process ofdyeing cellulose-based materials, comprising the steps of:(a) providinga dye composition prepared according to claim 1; (b) immersing saidcellulose-based materials in a container of water; (c) dissolving saiddye composition in a separate container of water, producing a dyesolution; (d) adding to said dye solution sodium sulfate and an acidiccompound; and (e) soaking said cellulose-based materials in said dyesolution and heating said solution to produce colored cellulose-basedmaterials.
 16. A process of preparing a dye composition, comprising thesteps of:(a) treating aniline with acid and a source of formaldehyde toform methylenedianiline; (b) oxidizing said methylenedianiline by addingan oxidation catalyst, aniline, and an oxidant, wherein the reactionproduces a mixture comprising pararosaniline and oxidation products; (c)separating said oxidation products from pararosaniline to produce anaqueous solution of oxidation products; (d) adjusting the pH of saidsolution to at least about 10.5 by adding a basic compound and water;(e) separating unreacted aniline from said solution of oxidationproducts to form a mixture of oxidation products; (f) treating saidmixture of oxidation products to form a powder; and (g) sulfonating saidpowder to form a dye composition.
 17. A process according to claim 16,wherein said acid is selected from the group consisting of hydrochloricacid, anhydrous hydrogen chloride, aqueous hydrochloric acid, aceticacid, and mixtures thereof.
 18. A process according to claim 16, whereinsaid methylenedianiline is an isomer selected from the group consistingof 2, 4-methylenedianiline, 4, 4'-methylenedianiline, and mixturesthereof.
 19. A process according to claim 16, wherein said source offormaldehyde is selected from the group consisting of formalin solution,gaseous formaldehyde, solid paraformaldehyde, and mixtures thereof. 20.A process according to claim 16, wherein said oxidation catalyst is avanadium oxide catalyst.
 21. A process according to claim 20, whereinsaid vanadium oxide catalyst is selected from the group consisting ofsodium metavanadate, ammonium metavanadate, vanadium(IV) oxychloride,vanadium(V) oxychloride, and mixtures thereof.
 22. A process accordingto claim 16, wherein said oxidant is selected from the group consistingof air, oxygen, oxygen enriched air, and mixtures thereof.
 23. A processaccording to claim 16, wherein said oxidation products are based on thestructures of compounds selected from the group consisting of acridines,phenazines, phenosafranines, aniline blacks, and mixtures thereof.
 24. Aprocess according to claim 16, wherein said separation step (c) iscarried out by:(a) adjusting the pH of said mixture to about 7 bytreating said mixture with a basic compound and water; (b) convertingsaid pararosaniline to an insoluble form with an anion selected from thegroup consisting of nitrate, bisulfate, cyanide, and mixtures thereof;and (c) filtering said solution to remove said pararosaniline.
 25. Aprocess according to claim 16, wherein said separation step (c) iscarried out by:(a) adding to said mixture a solvent in whichpararosaniline is insoluble and in which said oxidation products aresoluble; and (b) filtering said solution to remove said pararosaniline.26. A process according to claim 25, wherein said solvent is a benzeneor alkyl-substituted benzene compound.
 27. A process according to claim16, wherein said sulfonation step (g) is carried out by adding sulfuricacid to said powder and heating said powder and sulfuric acid to fromabout 40 to about 90° C.
 28. A process according to claim 16, whereinsaid basic compound is sodium hydroxide.
 29. A process according toclaim 16, wherein said pH of said solution is from about 12 to about13.8.
 30. A dye composition prepared according to the process ofclaim
 1. 31. Colored protein-based fibers prepared according to theprocess of claim
 14. 32. Colored cellulose-based materials preparedaccording to the process of claim 15.